Heretofore, authentication of documents relied primarily on various seal devices and on the examination of original signatures. These basic authentication techniques prevented an electrostatic copy of record document from passing as the original document. However, seals may be cleverly altered, transferred to other documents or counterfeited; and experienced forgers can produce high quality forgeries of signatures which are difficult to detect even by qualified handwriting experts.
These prior seal and signature safeguards did not involve any unique quality of the underlying paper. Nor were seals and signatures typically employed on every sheet of a lengthy document.
Unique surface texture has been employed to authenticate hotel room keys against unauthorized duplicates, as taught in U.S. Pat. No. 4,677,435 issued on Jun. 30, 1987 to D'Agraives et al. The surface texture in a predetermined seal area on the room key was initially scanned and stored in a central computer with an initial texture databank at the front desk. Each time the quest inserts his key to enter his room, a small scanning device in the door lock rescans the seal area and transmits the new texture data immediately to the central databank. If the new texture data compares with the initial data, the door can be opened by the quest. If the new data does not compare, an override lock controlled by the central computers prevents entry.
Conductive fibers have been randomly distributed throughout a document to produce a unique conductive pattern, as taught in U.S. Pat. No. 4,820,912 issued on Apr. 11, 1989 to Roeselare. The fiber pattern was scanned by microwave energy to establish initial reference data which was later compared to subsequent data for authentification.
The unique translucency pattern of a paper tag (or identification card) has been employed to authenticate the tag, as taught in U.S. Pat. No. 4,423,415 issued on Dec. 27, 1983 (and U.S. Pat. No. 4,476,468 issued on Oct. 9, 1984) to Goldman. The initial translucency data from a tag seal area was magnetically stored on an "escort" memory carried on the paper tag. Later the seal was rescanned and the new translucency data was compared to the magnetic initial data.